Porous pipe for underground irrigation systems eliminates the need for sprinkler heads and the resultant objections thereto in the manipulation of lawn care equipment such as mowing, aerating and shut-down time when in use. With a porous pipe irrigation system, water is delivered directly to the root area of plants and can be applied at any time in amounts determined by the degree of porosity in the pipe. A method of forming extruded porous pipe for this general purpose is disclosed in U.S. Pat. No. 4,110,420 wherein the pipe is formed of reclaimed particle sized rubber material mixed with polyethylene, with the flow passages in the pipe wall being the result of foaming with steam and gases released from the mixture and primarily from the reclaimed rubber. The degree of porosity is dependent upon the properties of the reclaimed rubber in the initial mix. By virtue of the particalized reclaimed rubber material, it is necessary to initially screen the material to size and then use relatively high extruding pressures of 2,000 to 3,500 psi at temperatures, during extrusion, varying between 300.degree. and 400.degree. F. to plasticize the polyethylene to a fluid plastic state while retaining the integrity of the prevulcanized reclaimed rubber material.